This theory has been doing the rounds on Twitter and fan forums for the past few days – and it certainly seems to be a likely possibility. Why? Well, for starters, Michelle's husband Tim, and son Mark, both appear to be avoiding her calls. She is drinking quite a bit. And we know that she's broken that law (thanks to a certain trailer).

But more to the point, who just spontaneously ups and leaves their family on Christmas Eve unless some serious drama had gone down? Let's face it, this is the woman that didn't even fly back to attend her mother Pauline's funeral. Everything seems to indicate Michelle having done something so bad that her family – and possibly even Sharon, too – can't forgive her. Given that Sharon is hardly in a position to judge her friend for having an affair, throw in a student - and everything seems to fall into place, don't you think?

We're going to be honest, when it was first revealed that Michelle had returned to Walford with a secret, our first thought what that she had a life-threatening disease. It seemed to match the soapy criteria of a character returning to her old home after all this time, only to announce they are terminally ill (see Donna inEmmerdale). But then that trailer was unveiled, and everything changed.

Michelle's secret now appears to be more self-inflicted as opposed to illness related, but we are not ruling it out completely. Could it be that her illness has run Michelle into money difficulty? Perhaps she doesn't have health insurance? Or perhaps she has been paying for expensive treatment?

That said, Sharon appears to react badly to Michelle's news in the brief clip we've seen, and we can't see her being so hostile if her bezzie really was ill. So maybe we just need to accept that our initial theory was wrong.

Could Michelle's dark secret be that she is harbouring a difficult, and complex, alcohol addiction? It would make her upcoming heart to heart with Sharon all the more poignant, given her husband Phil's plight. And it could also be why she feels Sharon is the only one to help her.

Obviously this doesn't explain why she can be seen telling Sharon she's broken the law, but it could be that her addiction has taken her down a dangerous track. Maybe she did something illegal whilst under the influence? Maybe she's been stealing booze?

Or maybe, she has been splashing out on so many bottles of champagne, and fancy red wines, that she has driven her family into debt? After everything she's been through with Phil, we can't see Shazza being too understanding about this one.

4. She's in some other form of debt

While this would seem a little dull, it is still entirely plausible. Instead of alcohol being the cause of the debt problem, it's likely that the stress of the debt has led Michelle to alcohol. Last night's episode hinted that Michelle could be strapped for cash after we saw her pay a visit to the cash brokers prior to attending her leaving party in the Vic.

It also hasn't gone unnoticed Michelle has a (rather annoying) habit of dropping her wealth into conversations every five minutes, but could it be that she is simply trying to keep up appearances? Hot tubs, cleaners, fancy towels, and publicly ordering three bottles of champagne – Michelle certainly seems to be trying to live up to the image of someone with a very comfortable lifestyle back in America.

However, with Michelle simultaneously paying visits to brokers, something certainly doesn't add up. So, could her big secret be that she's got herself into a worrying amount of debt, and has to go to desperate measures to get herself out of it?

Forget alcohol, affairs, debts. Could it be that Chelle is actually a notorious criminal over in the States? It could explain why she has kept her distance for so long – she's been knee-deep in scandal. What would Pauline say?

According to Sharon, Michelle doesn't know that Mark has been told the truth about Grant. But what if this is all a lie? What if all hell has broken loose in America over Mark's discovery that Grant is his father and Michelle has come back to Walford to settle some scores? If it means we will get to see Grant again sometime soon, then we aren't complaining. But sadly, this doesn't seem very likely. So it's back to the drawing board...